Periodontal disease is an inflammatory process characterized by vascular dilation, increased microvascular permeability, migration and infiltration of inflammatory cells. These events may result in eventual loss of periodontal attachment. Bone resorption in periodontitis is due to an increased activity of osteoclasts. Recently, a very potent mediator of inflammation, platelet-activating factor (PAF, PAF-acether, AGEPC), has been discovered. In other systems, PAF has been shown to produce almost all of the underlying characteristic lesions observed periodontal disease. However, its role in the development of the periodontal disease has note been studied. It is our hypothesis that PAF is involved in activation of osteoclasts leading to bone resorption and progressive destruction of structures supporting the tooth. IN order to test our hypothesis, we will do the following: 1. We will examine the effect of PAF and selective antagonists of PAF receptors in vitro on bone resorption capacity of osteoclasts which will be isolated in primary cultures, and 2. We will identify and characterize PAF receptors on osteoclasts. These studies will be a definitive test of the effect of PAF on bone resorptive capacity of osteoclasts under in vitro conditions.